Field of the Disclosure
This disclosure relates to components for turbochargers driven by exhaust gas. More particularly, this disclosure relates to barrel or piston type wastegate valve designs with a cylinder having a through hole used in a turbine housing.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber in a controlled manner. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbine includes a turbine wheel that is mounted on a shaft and is rotatably driven by exhaust gas flow. The turbocharger returns some of this normally wasted exhaust gas energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is driven by the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine. The compressor includes a compressor impeller that is mounted on the same shaft so that rotation of the turbine wheel causes rotation of the compressor impeller.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. The turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold.
This disclosure focuses on a wastegate valve disposed in the turbine housing of turbochargers. A wastegate (WG) valve assembly includes a valve, vent and/or bypass that is able to route a significant portion (an example being about 30 percent) of the exhaust gas around (i.e. bypassing) the turbocharger turbine, in order to limit/control turbine work, thus only utilizing a fraction of the available exhaust energy when appropriate. Thereby, the WG valve assembly regulates exhaust gas flow and ensures that the turbine wheel is not spun at an undesirable speed.
For a fixed geometry turbocharger (i.e. no WG), the turbine must be chosen such that at rated conditions (high engine speed, max power), the turbine wheel speed is not excessive. However, this usually means that at peak torque condition (medium engine speed, max torque), the turbine housing is undesirably large, impacting negatively on transient response and engine torque. To strike a better compromise between peak torque and rated conditions, a wastegate is often employed. A wastegate selectively allows a portion of the exhaust gas flow to bypass the turbocharger, specifically the turbine, thereby governing the amount of energy that is extracted from the available exhaust gas flow.
Decreasing the amount of opening of the wastegate valve reduces the amount of exhaust gas flow that is allowed to bypass the turbine, which should increase pressure of the air entering the intake manifold. An actuator for the valve can adjust whether exhaust gas bypasses the turbine through the wastegate.
A wastegate valve may be operated in a conventional way, for instance by a pneumatic actuator or electric actuator to allow some of the exhaust gas flow to bypass the turbine. As a result of higher demands and increased loads, the exhaust temperatures, pressure conditions, and stress on wastegate valves and actuators have increased.
Conventional wastegate valves can be complex with numerous parts. Such wastegate valves substantially operate in an on/off function.